The necessity to support the roof and underground cavities during underground excavation is well known in the art. One such example of underground excavation which requires that the roof be supported is commonly referred to as "pillar extraction" and is frequently used in the recovery of underground coal deposits. In such pillar extraction methods, it is desirable to cave the roof under controlled conditions behind the working face.
Generally, during pillar extraction, it is desirable to support the roof in several locations in order to insure the safety of the individuals in the mine and to protect expensive mining equipment from damage as well as to prevent costly delays of the mining operation. There are several methods currently used for supporting the roof during pillar extraction. One such method involves the use of two pairs of conventional mobile roof supports at two specified locations. In particular, one pair is generally positioned in a cross-cut adjacent one end of a mining device such as a continuous miner. The second pair is located in the entry to the pillars to support the roof and generally provide an additional escape path in the event of an emergency. One problem associated with only using two sets of conventional roof supports is that a portion of the roof adjacent the continuous miner is unsupported, leading to a possibly dangerous environment for the workers and the machinery. In order to increase efficiency and decrease travel time of the conventional roof supports a third pair of roof supports may be positioned in another entry. The second and third pair of roof supports alternately move to successive entries to allow the continuous miner to successively extract pillars without interruption as a result of a roof support having to be moved to another entry. Each pair of mobile roof supports generally work together, one supporting the roof while the other is advanced a predetermined distance to support an adjacent area of the roof.
Conventional mobile roof supports are well known in the art and are quite expensive and may cost several hundred thousand dollars each. In addition to the cost of conventional roof supports, operations of the several pairs of roof supports can become complicated as each of the mobile roof support units must be moved independently of the other units which may require, for example, six separate remote control channels. Hand held remote control units are generally limited to four channels thus requiring the use of two hand held units when operating more than two pairs of conventional roof support. Coordinating such movement is difficult and time-consuming and the failure to properly coordinate such movement could potentially prove to be dangerous.
Some prior art devices have attempted to reduce the number of roof supports necessary by coupling essentially identical units together and operating them in tandem. This has however, not reduced the expense nor complexity associated with using mobile roof supports. Moreover, when these coupled units are not in use and need to be transported to other locations in the mine, they are often difficult to maneuver in the narrow confines of the mine environment. Additionally, uncoupling the units to allow transport may result in an exceedingly difficult task that delays the efficient use of the roof supports and other mine equipment.